According to the present state of the art, tractors with front loaders, such as wheel loaders, telescope loaders, crane vehicles, and similar land vehicles are provided with suspension/shock-absorbing systems that consist of one or more gas-filled hydraulic-storage units, which are connected as needed to a hydraulic stroke cylinder of one of the booms, in order to reduce the effects of vibrations of the boom on the chassis of the vehicle and vice versa. In this connection, we speak of “passive” suspension systems. They have the disadvantage that they are based, as a rule, on a constant suspension characteristic and thus their suspension characteristics do not react in a variable manner to the load acting on the stroke cylinder or the boom. A suspension that acts variably depending on the load can be achieved using hydraulic-storage units only by means of expensive nozzles and valve systems.
An example of such a passive suspension system is disclosed in DE 42 21 943 C2. In it, a hydraulic system for a drivable working machine with working devices is recommended with a load-suspension system consisting of at least one hydraulic-storage unit. In order to balance the load pressure of the hydraulic-storage unit on the load pressure of a stroke cylinder at all times, at least one nozzle is envisioned in connection with several path valves between the load-suspension system and the stroke cylinder. This system is expensive and takes up space.
“Active” vibration dampers have been known for some years from rear power lifters on agricultural tractors. These “active” damping systems measure the loads that are affecting the vehicle because of vibrations and shifts the loads according to the stroke cylinder of a power lifter in such a way that the stimulating vibrations are counteracted, which weakens the stimulating vibrations. Since the power lifter of the hydraulic system is lifted and lowered actively, depending on the load condition, we speak of an “active” elimination of vibrations.
An “active” vibration-damping system is disclosed in DE 100 46 546 A1. In it, a large manipulator is recommended with a vibration damper that has means for damping mechanical vibrations in a concrete-pumping system in a folding boom of a concrete pumping system. The vibration damper charges the pressures in the individual hydraulic cylinders of the folding boom of the concrete-pumping system in such a way that the end piece, out of which the liquid concrete flows, stays in its position relatively calmly. This vibration-damping system is very expensive, since each hydraulic cylinder must be provided with two pressure sensors and each folding link with an angle of rotation sensor. In addition, a very complex control algorithm is used, which is unsuitable for the active suspension of a boom of a loading vehicle.
DE 100 06 908 A1 discloses an agricultural working machine that is connected on its front to a telescoping boom. The boom is raised or lowered by a hydraulic piston-cylinder unit. To realize a pre-selectable force to be applied to a moving device taken up by a boom, a hydraulic circuit is recommended that has a seat valve that can be blocked and an adjustable pressure-control valve, so that a uniform pressure is maintained in a cylinder space on the piston side and the same force is always applied to the bottom, specifically, regardless of whether bottom is even or uneven. It has the disadvantage that the recommended hydraulic circuit is set only to a pressure limit that can be set in advance and thus is not suitable in form for an active suspension system.
The task on which the invention is based is seen as providing a hydraulic suspension of the type mentioned by which the problems mentioned above can be overcome. In particular, an active suspension is created that reacts variably to the load conditions of a boom of a loading vehicle.